Research is proposed to address heterogeneity in childhood Attention- Deficit Hyperactivity Disorder (ADHD) via a first study of neuropsychological performance in relatives. ADHD represents a substantial public health problem: It is common, leading to extensive use of mental health services, and chronic, markedly increasing risk of future learning, adjustment, substance abuse, and criminal problems for these children. Identification of standard, noninvasive trait markers of risk in family members is underutilized with ADHD. Discovery of such markers, and identification of the characteristics of the subgroup to which they apply, would increase chances of understanding etiology and enable better assessment, intervention, and prevention for this costly disorder. By neuropsychological assessment of parents, the study will extend ADHD family research into a new domain, and increase knowledge of family factors that shape the development of the disorder. An exploratory but important dimension of the study reflects theoretical considerations that link personality traits to both psychopathology and EFs. Like ADHD, key personality traits are familial and partially heritable, therefore they may amplify or confound the marker approach if not examined as well. To address this possibility, major parent personality traits, including Sensation Seeking will be examined. The study is based on theoretical considerations that implicate prefrontally-mediated neuropsychological Executive Functions (EFs) in ADHD) and recent empirical evidence that the crucial EF deficits in ADHD are (a) planning and (b) inhibition. Yet, if the "prefrontal" conjecture about ADHD is correct, other, less-studied prefrontal functions might differ in relatives also, especially semantic retrieval and non-verbal working memory. The hypothesis that these deficits may comprise subclinical markers of risk in family members will be tested by studying these critical EFs in 7-9 year olds with ADHD and comparison children and their biological parents. Mapping of deficits (if any) in parent would also help clarify which components of prefrontal operation are impacted. A community-based sample, recruited through invitations sent out from area schools, will complete structured diagnostic interviews, cognitive screening, and a theoretically and empirically-based EF battery in a laboratory visit. Because they could influence neuropsychological results, comorbid child disorders and parent psychiatric status will be carefully assessed and controlled.